1. Field of the Invention
The present invention relates to semiconductor devices, manufacturing methods of the same, and semiconductor manufacturing apparatus, in particular, for being suitably applied to a so-called system-on panel, in which a pixel region including thin film transistors and a peripheral circuit region including thin film transistors are formed on a non-crystallized (amorphous) substrate such as a non-alkali glass substrate.
2. Description of the Related Art
A TFT (Thin Film Transistor) is formed on a very thin, fine active semiconductor film. The TFT is examined to be mounted on a large-screen liquid crystal panel or the like in consideration of recent demands for an increase in area. In particular, applications to a system-on panel and the like are expected.
On the system-on panel, polycrystalline semiconductor TFTs (especially polysilicon TFTs (p-Si TFTs)) are formed on a non-crystallized substrate such as a non-alkali glass substrate. In this case, as a popular method, an amorphous silicon (a-Si) film is formed as a semiconductor film, and then irradiated with an ultraviolet short-pulse excimer laser to fuse and crystallize only the a-Si film without influencing the glass substrate, thereby obtaining a p-Si film functioning as an active semiconductor film.
Excimer lasers which emit high-output linear beams coping with a large area of the system-on panel have been developed. A p-Si film obtained by excimer laser crystallization is readily influenced by not only the irradiation energy density but also the beam profile, the state of the film surface, or the like. It is difficult to form uniformly a p-Si film large in crystal grain size in a large area. A sample crystallized by an excimer laser was observed with an AFM to find that crystal grains isotropically growing from nuclei produced at random exhibited a shape close to a regular polygonal shape, projections were observed at a crystal grain boundary at which crystal grains collided against each other, and the crystal grain size was less than 1 μm, as shown in FIG. 37.
In this manner, when a TFT is fabricated using a p-Si film obtained by crystallization using an excimer laser, a channel region contains many crystal grains. If the crystal grain size is large, and the number of grain boundaries present in the channel is small, the mobility is high. If the crystal grain size at a channel region portion is small, and the number of grain boundaries present in the channel is large, the mobility is low. Thus, the transistor characteristics of the TFT readily vary dependently on the grain size. In addition, the crystal grain boundaries have many defects, and the presence of the grain boundaries in the channel suppresses transistor characteristics. The mobility of the TFT attained by this technique is about 150 cm2/Vs.